1. Field of the Invention
The present invention relates to a novel superconductive material, and more particularly, it relates to a ceramic superconductive material which is employed for a power product to which a superconducting magnet is applied, a Josephson device for a computer or an infrared sensor, etc.
2. Description of the Prior Art
The most significant property of a superconductive material is that the same enters a superconductive state at a higher critical temperature. This is because the obtained critical temperature determines the cooling medium to be employed and the range of practical use.
The critical temperature of a conventional superconductive material has been at about 23K at the best, while a cooling medium therefor has been generally prepared by liquid helium, the temperature of which is sufficiently lower than the critical temperature.
However, such liquid helium is high-priced, while a costly vacuum adiabatic vessel has been inevitably required in order to prevent evaporation thereof.
It has recently been recognized that certain ceramic materials show the superconducting phenomenon. Such a material is prepared by an oxide which is in K.sub.2 NiF.sub.4 type layer perovskite crystal structure generally expressed in a chemical formula (A.sub.1-x B.sub.x).sub.2 CO.sub.4-y. It has been confirmed that such a material shows a critical temperature of about 40K. However, this material still requires a cooling medium of high-priced liquid helium. On the other hand, an extremely low-priced cooling medium is prepared by liquid nitrogen, which has a boiling point temperature of 77K. Thus, such low-priced liquid nitrogen can be employed in place of liquid helium for a superconductive material having a critical temperature of at least 77K, to extremely widen the range of practical superconduction.